Classifications

• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B11/00—Calcium sulfate cements
  • C04B11/02—Methods and apparatus for dehydrating gypsum
  • C04B11/028—Devices therefor characterised by the type of calcining devices used therefor or by the type of hemihydrate obtained
  • C04B11/032—Devices therefor characterised by the type of calcining devices used therefor or by the type of hemihydrate obtained for the wet process, e.g. dehydrating in solution or under saturated vapour conditions, i.e. to obtain alpha-hemihydrate
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B11/00—Calcium sulfate cements
  • C04B11/02—Methods and apparatus for dehydrating gypsum

Definitions

• the invention relates to the construction material industry and can be used for producing gypsum binders and products made on their basis.
• the principle of obtaining gypsum binders is based on a capacity of calcium sulfate dihydrate, when heated, to undergo dehydration accompanied by changes in the crystal lattice structure (re-crystallization).
• ⁇ - and ⁇ -modifications of gypsum are characterized by the same crystal lattice type. Their difference is that the first has a better structure with well-defined large-size crystals, while the second consists of smallest aggregates of defective crystals with a developed inner surface.
• ⁇ -gypsum products show much better characteristics of strength and moisture resistance than ⁇ -gypsum products.
• the primary production volume of gypsum binders falls into ⁇ -hemihydrate, owing to its simpler and cheaper production technology.
• the last two processes relate to processing in a liquid medium and use additional steps of washing and drying. This consumes a large amount of water and additional heat. This is a significant disadvantage of these methods. Therefore of great practical importance are methods of processing in a gaseous medium, eliminating the need for washing and further drying.
• Construction gypsum ( ⁇ -gypsum) is obtained using a simple technology by heat treatment of gypsum raw material at normal pressure within the temperature range 100° C.-160° C.
• ⁇ -modification of gypsum is the technological simplicity that does not require high pressurization and low cost. Nevertheless, ⁇ -modification of gypsum, obtained using these methods, is characterized by poor strength properties, no moisture resistance and short mixing time.
• gypsum-based mixtures In order to improve gypsum binder properties, depending on required characteristics, multi-phase (i.e., from diverse modifications of gypsum) and/or composite (with adding external non-gypsum components) gypsum-based mixtures are produced. Their production involves varying the composition, granulometry, and the component ratio for regulating functional properties: durability, setting time, water resistance, etc. There are great many various additives affecting properties of gypsum binders. All this greatly increases the cost of the finished product.
• gypsum binder described in RU patent No. 2023699 published on Nov. 30, 1994, which suggests a method of producing a binder with predominating calcium sulfate ⁇ -hemihydrate.
• the method consists of gypsum dehydration carried out in lumps at atmospheric pressure, in a gaseous medium its important advantage is in use of an electromagnetic super-high-frequency field (SHF field). Due to volumetric heating affected by SHF radiation, dehydration with development of predominantly ⁇ -modification of gypsum occurs in the proper volume of a lump, which becomes a sort of “mini autoclave” for itself. ⁇ -modification of gypsum develops in the near-surface layer.
• SHF field electromagnetic super-high-frequency field Due to volumetric heating affected by SHF radiation, dehydration with development of predominantly ⁇ -modification of gypsum occurs in the proper volume of a lump, which becomes a sort of “mini autoclave” for itself. ⁇ -modification of gy
• the present invention is related to a method for producing gypsum binders and products made on their basis that substantially obviates one or more of the disadvantages of the related art.
• a method of producing a gypsum binder including dehydrating of gypsum raw material lumps by heating in a gaseous medium with further drying, cooling, and milling stages, wherein the heating gypsum raw material lumps is performed either by: (i) placing the lumps in a heating medium set to a temperature exceeding the temperature under which dehydration and formation of gypsum ⁇ -hemihydrate occurs; or (ii) placing the lumps in a heating medium having a high rate of temperature increase such that a temperature higher than the temperature under which dehydration and formation of gypsum ⁇ -hemihydrate occurs is reached; wherein a heating time is selected sufficient for completion of the process of gypsum ⁇ -modification formation within the gypsum lumps, and wherein the heating is performed under atmospheric pressure through lump surface.
• gypsum raw materials natural gypsum stone and/or synthetic gypsum, and/or recycled gypsum are used as gypsum raw materials.
• lumps of gypsum raw material are formed by crushing and/or agglomerating.
• the heating medium temperature and heating time are determined experimentally for a particular raw material, depending on the size of lumps, properties of gypsum raw material and pore structure of the end product.
• the heating medium temperature is 140° C. to 600° C.
• the temperature of the medium for the drying stage is 100° C. to 400° C.
• the heating and drying stages are combined.
• the drying and/or cooling and/or milling stages are combined.
• the heating time is selected from 20 minutes to 5 hours depending on a size of the gypsum lumps, and properties of the gypsum raw material.
• the surface of gypsum raw material lumps is blown during the heating stage.
• the heating medium humidity is changed.
• a surface of the gypsum raw material lumps is pre-moistened.
• the method further includes over-pressurizing at the heating stage and/or under-pressurizing at the drying and cooling stages.
• the method further includes milling wherein fractions of the lumps near-surface layer and central part, rich in gypsum ⁇ -modification, are separated.
• the method further includes introducing additives, affecting the recrystallization process, into the composition and/or on the surface of agglomerated and/or lumpy raw material.
• the method further includes covering the surface of lumpy or agglomerated raw material with a coating that changes properties of surface pores.
• the method further includes, during processing, exposing raw material to SHF radiation in order to change recrystallization parameters.
• the method further includes obtaining a dehydrated gypsum ⁇ -hemihydrate or a soluble ⁇ -anhydrite with their subsequent reduction to gypsum ⁇ -hemihydrate.
• the technical result of the present invention is obtaining ⁇ -modification of gypsum and multi-phase gypsum binders based on using lumpy raw material, at atmospheric pressure in a gaseous medium.
• the technical result is achieved due to the fact that, in the proposed method involving dehydration of gypsum raw material lumps by heating at atmospheric pressure, heating of gypsum raw material lumps is carried out by placing them in thermal shock conditions and for a period required for completion of the dehydration reaction with predominating formation of ⁇ -modification of calcium sulfate hemihydrate, with further drying, cooling, and milling.
• Thermal shock conditions, or fast external heating by placing the lumps in a high-temperature environment and/or by ensuring high growth rate of ambient temperature around the lumps, the favour growth of water vapor pressure within a lump, which is necessary for dehydration with formation of, mainly, gypsum ⁇ -hemihydrate.
• Thermal shock is understood as characterized either by treating at high temperatures or high speed of temperature increase, or fast increase of temperature to the values above normally used values.
• the thermal shock suggests that the amount of energy, applied to raw material, is greater than energy required for transformation processes in used raw materials at every instant, i.e., energy is supplied in excess of its consumption.
• each lump becomes mini-autoclave for itself and conditions for dehydration with formation of gypsum ⁇ -modification are created within every gypsum lump.
• Such conditions are not established in the near-surface layer of a lump, and ⁇ -modification of gypsum develops there.
• thermal shock must be understood as such conditions of heat treatment of raw material lumps at the atmospheric pressure, under which the dehydration process occurs with ⁇ -recrystallization.
• Thermal shock parameters and time of the process are determined in advance, depending on properties of a specific raw material, size of lumps, and requirements to the end product as to the ratios ⁇ - and ⁇ -hemihydrates or other gypsum modifications in the end product.
• the heating stage implies dehydration and recrystallization
• the drying stage product dewatering
• cooling product cooldown
• the temperature of the gaseous media for thermal shock, drying, and cooling is selected from a technically feasible range, so that this technological stage can be carried out.
• the temperature of thermal shock medium is selected from the range 140° C. to 1200° C.
• the process of dehydration with ⁇ -recrystallization must progress within a lump at a specific temperature during a specific time period.
• the drying temperature can range from the ambient temperature to the thermal shock temperature. What matters is that, at this temperature and during this time period, a dehydrated product should lose moisture and no rehydration process should occur.
• the process time can vary from 15 minutes to 5 hours.
• This method can be used for processing raw material with naturally determined temperature and does not require preheating or cooling of the raw material.
• Gypsum raw material lumps can be formed by both crushing natural gypsum rock and by agglomerating powders and/or fine fractions of natural, synthetic, or recycled gypsum.
• Lumpy raw materials of sizes customary for the gypsum industry are processed; meanwhile, other process conditions, leading towards the needed result, are adjusted to specific raw material parameters.
• the production can be both continuous and periodic.
• the thermal shock and drying stages can be combined.
• drying and/or cooling, and/or milling stages can be combined simultaneously and/or in one device.
• Blowing of raw materials during dehydration process increases the content of gypsum ⁇ -modification in the near-surface layer of the lumpy gypsum.
• Milling using the surface abrasion method allows separating the product from the near-surface layer with an increased content of gypsum ⁇ -modification and the product from the middle of a lump with predominating content of gypsum ⁇ -modification.
• Preliminary surface treatment of gypsum raw material lumps to modify the pore structure, e.g., extra coating, will change the process modes and properties of the resulting product.
• the suggested method can also be used for production of dehydrated ⁇ -hemihydrate of gypsum or soluble ⁇ -anhydrite with their subsequent reduction to ⁇ -hemihydrate of gypsum. Insoluble anhydrite can also be produced.
• the process parameters can be chosen so that the finished product contains the active lime.
• Varying the process parameters allows obtaining gypsum binders with diverse compositions and changing the ratio of ⁇ - and ⁇ -modifications, hemihydrate, and anhydrite in a wide concentration range directly within the production process.
• samples of natural gypsum lumps, agglomerated in lumps and dried calcium sulfate dihydrate powder were used as a source raw material.
• the size of the lumps was 3-6 cm.
• the treatment process using the thermal shock method was carried out at atmospheric pressure by placing the gypsum raw material in a medium with the hot air under isothermal conditions at temperatures ranging from 160° C. to 360° C.
• the baking time was varying from 45 minutes to 3.5 hours.
• Table 1 summarizes the data of the Rietveld method for quantitative X-ray phase analysis and assessment results of calcium sulfate hemihydrate ⁇ -modification for several samples obtained by combining the thermal shock and drying processes.
• the treated samples represent hemihydrate gypsum with a certain content of impurities inherent with the source raw material; and presence of small amounts of anhydrite and calcium sulfate dihydrate was observed in some cases.
• the obtained end product samples represent hemihydrate gypsum with the ratio of ⁇ -modification to ⁇ -modification up to 95%.
• An essential advantage of this invention is its environmental benefit.
• the suggested method is easily applicable for processing of gypsum raw material, being a by-product of many industries implemented, largely, to reduce sulfur emissions.
• the recommended method does not require the stage of washing using lots of clean water, as needed for the solution technology of obtaining ⁇ -gypsum in the presence of an electrolyte.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Ceramic Engineering (AREA)
• Materials Engineering (AREA)
• Structural Engineering (AREA)
• Organic Chemistry (AREA)
• Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)

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• 2014
  • 2014-10-13 WO PCT/RU2014/000766 patent/WO2016060580A1/ru active Application Filing
  • 2014-10-13 EA EA201790812A patent/EA029596B1/ru not_active IP Right Cessation
  • 2014-10-13 US US15/518,893 patent/US9926228B2/en not_active Expired - Fee Related
  • 2014-10-13 EP EP14904036.2A patent/EP3208248A4/en not_active Withdrawn

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